hi paul and spencer that is really interesting on those filters not having the antisiphoning vlv in them , i have never cut one open myself , but was allways told by the japaneze people we dealt with that they did have them to prevent the exact problem that spencer was having , as they tended to bleed down sometime when the eng was shut off,, now the weird part we will have to get spencer to do this one , first paul is the filters you are using from isuzu silver in color , if so these are the filters that are supplied to the parts dirtribution supply , the filters that i got for spencer are the same filter that was used only for original assembyline installation, when the engs were new , and they are a bluish green , do they have the antidrain back vlv , i really don,t know ,i know they are suppossed to , i hope to find out , i sorta stumbled on a supplier of these accidently , why were they diff, in color , was so that in case of eng failure during the warrenty period, and after the milage interval that they were suppossed to be changed . if they were still the blue filter, you just could have had a problem with the warrenty people as this particular filter was not made available for parts distribution, this filter seems to be a bit heavier than the silver one, maybe imagination ,have not weighed one , would like to know for sure on the blue filter , so Spencer it is your turn to cut one open , i don,t have the heart to cut a new one , oh if you need any more i got 6 more in the other day along with the fuel filters Jerry